The Corinthians were not able to function well as Christians because they were "infants in Christ" (1 Cor 3:1). They were spiritually retarded because of spiritual malnutrition, for they could not take solid food (1 Cor 3:2). They were malnourished because they were divided (1 Cor 3:4), and vice versa. Division results in spiritual malnutrition, retardation, and deprivation. Thus, division is an extremely serious problem and sin.
Therefore, Jesus is praying that we be one as He and the Father are one (Jn 17:21). We must "make every effort to preserve the unity which has the Spirit as its origin and peace as its binding force" (Eph 4:3). We must forgive each other or not be forgiven by God (Mt 6:12). We are called to be ministers of reconciliation (2 Cor 5:18), even to the point of laying down our lives for one another (see Jn 11:51-52). "If you bring your gift to the altar and there recall that your brother has anything against you, leave your gift at the altar, go first to be reconciled with your brother, and then come and offer your gift" (Mt 5:23- 24).
"Behold, how good it is, and how pleasant, where brethren dwell at one!" (Ps 133:1) Behold, how bad it is, and how deadly, where brethren do not dwell at one! Be one. Go to Communion. Be in communion. Be one through, with, and in Jesus.